Psoriasis is common skin disease which is caused by an accelerated replacement of human skin cell. In normal condition, skin cells shed and replace themselves in 21-28 days. But in psoriasis, this process can occur in 2-6 days. Psoriasis can affect any ages, any gender and regardless the race. Around 125 million of people around the worlds are affected, or 2-3% of population is living with psoriasis.
Psoriasis is non-contagious from person to person or between the patient's body part itself. Up to now, there is no solid inference that psoriasis can run in families. Several cases show that children whose parent is psoriasis patient also have psoriasis. But some cases reveal the opposite.
The lesions vary in appearance with the type of psoriasis. About 80% of psoriasis case is plaque psoriasis. This type sometimes is also named psoriasis vulgaris as it means common. Plaque psoriasis lesions have silvery white scales, which are due to skin shedding (effect of accelerated skin growth). The redness of the lesions is due to the increase of blood vessels to support the increase of cell production.
Recent research has found that the change in skin growth is affected by the change in immune system. Certain immune cells (T cell) are triggered and become overactive. T cells act as if they are defending against virus infections or healing skin wounds. This condition accelerates the skin growth causing thick plaque to be formed. Psoriasis usually occurs in knee, elbow, and scalps, but it can also happen in any part of human body. Psoriasis has been shown to have significant impact on quality of life. Due to the appearance of the lesion, individuals with psoriasis are found to have low self-esteem.
There are four known types of treatments for psoriasis. The drug used depends on the severity level. For mild to moderate psoriasis, physicians give topical therapies. It is available in creams, lotions, ointments, mousses, and gels. The topical therapies are applied in localized psoriasis. The second treatment is phototherapy. This therapy uses ultraviolet light A (UVA) and B (UVB), and the phototherapy sessions can last for several weeks. The third treatment is systemic medication which uses tablets or pills. This treatment has potential side effects to the patient, hence only patients with moderate to severe psoriasis undergo this treatment. The fourth or the latest treatment found is biological injection. This treatment only applies t o patients with severe psoriasis which other types of treatment are not effective. The injection will block certain immune cells (T cell) to act, as this accelerated growth is the cause of psoriasis.
Physicians use their knowledge and experience to decide which treatment is to be applied. Patient's physical condition which differs from one another is also a consideration. The treatment therapy can include a combination of treatments with different dosages and depending on the patient's response, the treatment can be changed. Physicians assess the patient's psoriasis severity as well as monitor the treatment efficacy periodically.
The gold standard to assess psoriasis condition is Psoriasis Area and Severity Index (PAST). In PASI, the human body is divided into four body regions: head, trunk, upper extremities and lower extremities. There are four parameters to be determined at the body regions, namely area, erythema (redness), thickness and scaliness of the lesions. Severity is rated for each index on a 0-4 scale (0 for no involvement; 4 for severe involvement) for erythema, thickness and scaliness while 0-6 scale for area. Each body region is weighted according to the proportion of body surface area (BSA). Head is weighted 0.1, trunk is 0.3, upper and lower extremities are 0.2 and 0.4 respectively. PASI score is determined using the following equation:PASI=0.1(Rh+Th+Sh)Ah+0.2(Ru+Tu+Su)Au+0.3(Rt+Tt +St)Al+0.4(Rl+Tl+Sl)Al     A =area (0-6), R=redness or erythema (0-4), T =thickness (0-4), S =scaliness (0-4).    h=head, u=upper extremities, t=trunk, l=lower extremities.
The total PASI score ranges from 0 to 72; higher score indicate more severe psoriasis condition. The treatment is considered effective if the PASI score is reduced by 75% from the initial score.
Although PASI is gold standard to assess the treatment efficacy, this method is tedious and thus rarely used in daily practice. Dermatologist has to assess all lesions and provide scores for each parameter.
Scaliness is one of the parameters of PASI scoring. The scaliness refers to the extent of coarseness of the scale resulting in the roughness of the skin surface. This is due to the amount of stratum corneum that is present on the surface of plaque psoriasis. In order to assess the scaliness of psoriasis lesion, dermatologists observe and feel (usually using the index finger) the lesion condition. For each body region, a representative lesion is chosen for assessment. Dermatologists use their knowledge and experience, and the above assessment procedure to determine the scaliness score. Alternatively, an average scaliness PASI score is determined by selecting the most common lesion in that area. This subjective assessment procedure leads to inter-rater and intra-rater score variations, inaccuracies and inconsistencies. Inter-rater variation is the different scores given by two dermatologists, while intra-rater variation is the different scores given by same dermatologist at different times. Even for one dermatologist, it is possible to have a different score for one lesion if a second assessment is conducted. The high variation in rating a patient from time to time would interfere in determining treatment efficacy. Thus, an objective evaluation of psoriasis lesion scaliness for PASI is needed.
Another method to determine skin surface roughness is by performing biopsy, whereby the said skin samples are cut and analyzed physically. The skin sample is imaged by using scanning electron microscopy to obtain 3D skin surface. This is not recommended because it involves physical removal of the said psoriasis lesion even before knowing the severity of the said lesion. If the severity is low enough that oral or ointment medication can cure said psoriasis lesion, then the initial step of cutting said lesion is really unnecessary.
The 3D-Stylus measurement system has also been used to measure surface roughness of skin. A replica of skin surface is required to represent the original skin surface. The system only measures the replica of skin surface, and it may not measure the original skin directly. Besides, the system needs a trained person to build skin replica for skin roughness measurement.
It is therefore advantageous if the assessment of psoriasis lesion scaliness for PAST is made objective, non-invasive and assessed in vivo. This is important in deciding the treatment efficacy, especially in clinical trials. It is yet another advantageous if the assessment could be used in daily practice and performed by regular physicians.
The present invention overcomes the above shortcomings by providing a method and apparatus for assessing data from digital images of psoriasis lesion for said psoriasis lesion scaliness by utilizing a developed computer vision system to obtain Psoriasis Area and Severity Index (PASI) parameters in particular.